In one aspect, this invention pertains to the reclamation of a titanosilicate from a deactivated oxidation catalyst comprising a titanosilicate having deposited thereon one or more catalytic metals and, optionally, one or more promoter metals. In another aspect, this invention pertains to the reconstitution of an active oxidation catalyst from a deactivated oxidation catalyst comprising a titanosilicate having deposited thereon one or more catalytic metals and, optionally, one or more promoter metals.
Titanosilicates find utility in catalysts for oxidation processes. As an example, the art recognizes the production of olefin oxides by the hydro-oxidation of an olefin with oxygen in the presence of hydrogen and in the presence of a catalyst comprising a titanosilicate having deposited thereon one or more catalytic metals. Likewise, the art recognizes the production of alcohols and ketones by the hydro-oxidation of an alkane with oxygen in the presence of hydrogen and in the presence of a similar catalyst comprising a titanosilicate having deposited thereon one or more catalytic metals. Catalytic metals for such oxidation catalysts include gold, silver, the platinum group metals, the rare earth lanthanides, and mixtures thereof. As an alternative example, the art recognizes the production of olefin oxides by the oxidation of an olefin with hydrogen peroxide in the presence of a catalyst comprising a titanosilicate and a platinum group metal, typically palladium. The aforementioned oxidation catalysts may also have deposited thereon one or more catalytic promoter metals, such as the elemental metals or ions of the alkali, alkaline earth, and lanthanide rare earth elements, and mixtures thereof.
Like most catalysts, the above-identified oxidation catalysts operate until totally spent or until the degree of deactivation renders the operation no longer economical. When that level of deactivation is reached, replacement or regeneration of the catalyst is necessary. Regeneration of a deactivated oxidation catalyst is typically effected by calcination under oxygen or air, as disclosed, for example, in WO 98/00414 and WO 99/00188. Disadvantageously, the calcination may not restore sufficient catalytic activity. Moreover, at some point the deactivated catalyst may not be capable of regeneration, at which time the catalyst must be replaced with fresh catalyst. Accordingly, a need exists in the art for an improved and economical method of regenerating or reconstituting a deactivated oxidation catalyst comprising a titanosilicate having deposited thereon one or more catalytic metals, and optionally, one or more promoter metals.
The art, as exemplified in WO 99/39827, discloses regeneration of a spent catalyst containing gold deposited on a titanium dioxide support, by contacting the spent catalyst with dilute acid, such as sulfuric acid, followed by drying and calcining the acid-treated catalyst. The disclosed method does not teach removing catalytic metals from the support, and the titanium dioxide is not reclaimed. The reference is also silent with respect to the stability of titanosilicates in the presence of acid.
Other art, exemplified by US-A1-2003/0228970, discloses regeneration of a spent titanosilicate catalyst, absent catalytic or promoter metals, by contacting the spent titanosilicate with an acid, such as nitric, hydrochloric, or sulfuric acid, at a pH less than or equal to 3, followed by washing, drying, and calcining the acid-treated catalyst. The reference is silent with regard to catalytic metals being deposited on or being removed from the titanosilicate.
The prior art methods of regenerating oxidation catalysts do not address the aforementioned problems of regenerating a catalyst comprising a titanosilicate having deposited thereon one or more catalytic metals and, optionally, one or more promoter metals. The inability of prior art methods to regenerate deactivated oxidation catalysts to a sufficient level of catalytic activity inhibits the use of such catalysts on a commercial scale. Accordingly, a need exists to find an improved method of reconstituting a spent or deactivated oxidation catalyst comprising a titanosilicate having deposited thereon one or more catalytic metals and, optionally, one or more promoter metals.